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Hydrology of Canada

Overview

Canada’s surface water resources are considerable, an estimated 7% of the world’s renewable water supply. The location and average flow of Canada’s largest rivers are presented on the map of Streamflow. This map indicates that approximately 60% of the country’s freshwater drains to the north, away from the 85 percent of the population living within 300 kilometres of our southern border.

Canada’s Hydrologic Diversity

The diversity of Canada’s hydrology is a reflection of its bio-physical diversity, which can be generalized by the fifteen Terrestrial Ecozones.

The relatively wet, mountainous Montane and Boreal Cordillera and Pacific Maritime ecozones covering British Columbia, southwestern Alberta and much of the Yukon Territory form the western fringe of the country. High runoff from these ecozones drains westward into the Pacific Ocean - exceeding 3,000 mm annually in some coastal areas - and eastward into the vast, dry Interior Plains. The latter region comprises the flat, fertile Prairies ecozone in the south and the Boreal and Taiga Plains ecozones to the north. Generally, runoff on the Plains averages well under 200 mm per year, especially in the south where it can average less than 50 mm.

Most of central and eastern Canada is covered by the rugged Boreal and Taiga Shield and Southern Arctic ecozones, for which annual runoff trends from 100 mm in the northwest to 800 mm in the southeast, to over 1000 mm along the Atlantic coast. Surrounded by the Shield, the extensive wetlands of the Hudson Plains ecozone drain northward into Hudson and James bays.

The humid Mixed Wood Plains ecozone of the Great Lakes-St. Lawrence River Valley encompasses the heavily populated area of southern Ontario and southern Quebec. Annual runoff ranges from as low as 200 mm in the southwest to over 600 mm in the northeastern end of the ecozone. To the east of the Mixed Wood Plains lies the rugged, wet Atlantic Maritime ecozone which covers all of the provinces of New Brunswick, Nova Scotia and the Atlantic provinces and a portion of eastern Quebec. Runoff increases significantly from west to east, varying from 600 mm annually in the western part of the ecozone to 2000 mm along the Atlantic coast.

In the far north, the desert-like Northern Arctic ecozone straddles the Northwest Territories and Nunavut. Few data on runoff are available in this ecozone, but in view of the very low precipitation (100-200 mm annually) annual runoff is considered to be very low also. Even less is known about runoff from the glaciated, mountainous Arctic Cordillera ecozone, most of which covers Nunavut’s east coast.

The climates of Canada range from continental in the south to boreal or subarctic in the mid-latitudes and arctic in the north. Maritime influences modify both the west and east coast climates, the east coast less, because of the predominantly eastward movement of interior air masses. Permafrost occurs throughout the mid- to northern latitudes. Annual precipitation varies from 50 mm in the far north to as much as 4000 mm on the Pacific Coast.

Regional Water Issues

The hydrologic and socioeconomic diversity that characterizes Canada makes understanding and managing its water resource and its aquatic environment a great challenge. The federal-provincial/territorial water quantity agreements were developed in response to the needs of water management and environmental issues in each region. The accompanying table summarizes the hydrologic characteristics and related issues in each province and territory. Data and information collected under the cost-sharing agreements are essential to those who must make decisions concerning these issues.